1. Field of the Invention
This invention relates generally to starter motors for internal combustion engines and, more particularly, is directed to a retainer assembly for a pinion gear of a starter motor for an internal combustion engine.
2. Description of the Prior Art
Conventional starter motors for internal combustion engines utilize a clutch which is slidably positioned on a shaft. In particular, during starting of the internal combustion engine, a solenoid assembly slidably moves the clutch into engagement with a pinion gear on the same shaft. The clutch and pinion gear then continue to move along the shaft until the pinion gear engages a ring gear of the engine for starting the latter. In order to precisely position the pinion gear with respect to the ring gear and thereby limit the extent of travel of the pinion gear on the shaft, a circumferential groove is formed on the shaft distally of the pinion gear and a snap ring is force-fit over the shaft and seats within the groove. A retaining ring is positioned in surrounding relation to the snap ring. With such arrangement, sliding movement of the pinion gear along the shaft is limited by the retainer assembly.
However, with conventional starter motors, it is necessary that the snap ring occupies only a limited angular extent so that it can be force-fit over the end of the shaft into the groove. In this regard, the snap ring is cut away so as to occupy generally a maximum angle of approximately 300.degree.. In some cases, such as with the starter motor used by the Ford Motor Company, the snap ring is semi-circular so as to occupy an angle of only approximately 180.degree.. However, because of the limited angular extent of the snap ring, there is a reduced area to resist the force of the pinion gear impacting upon the retainer assembly when the pinion gear is moved into engagement with the ring gear, than would otherwise occur with a snap ring extending the entire circumference of the groove. Accordingly, the snap rings used in conventional starter motors may not be capable of withstanding the impact forces from the pinion gear over a prolonged period of time, thereby cracking or breaking.